How to use in game engine

Unity

1. Export FBX from blender with binary(off Armature->AddLeafBones).

2. Drag and drop the FBX file to the Unity.

3. Set the Root to the rootnode.

Unreal

1. Set the frame rate 30fps.

Export FBX from blender with binary(off Armature->AddLeafBones).

2. Import the fbx file to 3dsMax with unit  as meter and chose Animation->Extra Options->Animation Take(usually *ArmatureAction), check Geometry->Smoothing Groups. 

3. Delete the dummy named Armature (the root object of the actual armature)

4.Export the FBX with unit as automatic, check Geometry->Smoothing Groups.

5.Drag and drop the FBX to UE4.

To import the animation check "Use default settings".

However, in the unit system of UE 4, the size of the mesh is about one hundredth.
The procedure to change the scale of the model is posted in the following article.
http://eizouasobi.blogspot.com/2019/01/how-to-change-scale.html

Animation editing within Blender

How to transfer root bone pose animation to the animation of the entire armature

https://eizouasobi.blogspot.com/2024/05/blender-python.html
How to bake action:
https://eizouasobi.blogspot.com/2024/04/how-to-bake-actions-in-blender.html
How to split action:
https://eizouasobi.blogspot.com/2024/04/how-to-split-actions-in-blender.html